The present invention relates to an improved X-ray tube of the type having a cylindrical, at least partially X-ray transmitting, vacuum envelope which is formed at least partially of metal and with the high voltage leads for the anode and the cathode disposed at the frontal or end surfaces of the envelope.
X-ray tubes for various applications are known to be operated with high direct or alternating voltages applied between the anode and the cathode, and depending on the desired radiation intensity, the voltages applied reach up to several 100kV. In such X-ray tubes, the necessary insulating paths are arranged predominantly in the axial direction.
In order to assure insulation of such X-ray tubes against ground, it is the custom to form so-called hood units which include a metallic jacket in whose cavity the X-ray tube is disposed and surrounded by an insulating medium which may consist of a gas, an oil or another solid substance. For operation with direct voltages these hood units are additionally provided with high voltage outlets through which the high voltage is fed to the X-ray tube by means of high voltage cables.
Depending on the type of tube, the anode may be electrically connected with the metallic jacket portion and may be grounded so that the cathode lies at a potential which is highly negative with respect to the outer wall of the hood, or the metal jacket of the hood portion may be grounded and the anode may have a positive voltage and the cathode a negative voltage compared to ground. These tubes are called single-pole and dual-pole X-ray tubes, respectively.
When X-ray tubes are operated with alternating voltage it is the custom to arrange the required high voltage transformer(s) together with the tube within the hood portion and likewise surround the transformers with an insulating medium.
In such known devices it is considered a drawback that
(a) the hood unit of necessity has a substantially larger diameter than the X-ray tube; PA1 (b) the dimensions of the outlets significantly increase the dimensions of the hood unit; and PA1 (c) upon a defect in the tube or in the high voltage leads or in the transformers it will generally be necessary to disassemble the entire hood unit which must then be refilled with insulating medium after careful evacuation, and consequently exchange of the defective part can be accomplished only in a service shop.